A third booster shot of the AstraZeneca-Oxford Covid-19 vaccine Vaxzevria significantly boosts antibody levels against the Omicron variant of the coronavirus, claimed the British drug major.
This brightens the scope for Serum Institute of India (SII), which makes Covishield, the Indian version of the Vaxzevria. Experts are of the opinion that mixing vaccine shots may give better results to boost immunity. However, the University of Oxford has supported the use of Vaxzevria as a third booster dose against Omicron. SII is sitting on 500 million doses of Covishield (half of which is in bulk drug form), and has cut production by half owing to low demand.
If the vaccine is recommended for use as a booster against Omicron, it may significantly boost the demand for Covishield in India. An Indian expert group on vaccination policy is yet to take a call on whether and when to allow Covid booster shots.
Vaxzevria was co-invented by the University of Oxford and its spin-out company, Vaccitech. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.
“Neutralisation titres for Omicron were boosted following a third dose with Vaxzevria compared to titres after a second dose. The levels seen after the third dose booster were higher than the neutralising antibodies found in individuals who had been previously infected with and recovered naturally from Covid-19 (Alpha, Beta, Delta variants and original strain),” AstraZeneca said.
It explained that sera obtained from individuals one month after receiving the third dose booster vaccination neutralised the Omicron variant to levels that were broadly similar to those observed one month after the second dose against the Delta variant. Two doses of Vaxzevria have been associated with protection against the Delta variant in real world studies, it added.
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The study analysed blood samples from individuals infected with Covid-19; those who had been vaccinated with a two-dose schedule and a third dose booster; and those who had reported previous infection from other Covid-19 variants of concern. The study included samples from 41 people who had received three doses of Vaxzevria.
The study was performed independently by investigators at the University of Oxford.
John Bell, Regius Professor of Medicine, University of Oxford, UK and one of the study investigators, said, “It is very encouraging to see that current vaccines have the potential to protect against Omicron following a third dose booster. These results support the use of third dose boosters as part of national vaccine strategies, especially to limit the spread of variants of concern, including Omicron.”
Sir Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca, said: “Vaxzevria plays an important role in vaccination programmes around the world and these data give us confidence that the vaccine should be given as a third dose booster.”
Data from another laboratory study supports Vaxzevria’s effect against Omicron, with individuals vaccinated with two doses of Vaxzevria retaining neutralising activity against Omicron, although a decrease was seen compared to the original strain.
AstraZeneca is collecting real world evidence evaluating the effectiveness against the Omicron variant with academic groups in the southern African region. AstraZeneca is also analysing blood samples from participants in the company’s phase II/III trial to evaluate neutralising activity when given as a third dose booster against Omicron for both Vaxzevria and its investigational next generation Covid-19 vaccine, AZD2816.
Data from these studies are expected soon.
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